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Fanning's nomination to the position had been held up in the Senate by Republican Kansas Sen. Pat Roberts

Washington (CNN)The Senate on Tuesday confirmed Eric Fanning to be secretary of the Army, making him the first openly gay secretary of a U.S. military branch.

Fanning said in a tweet Tuesday evening that he was "honored" by the confirmation.

Fanning's nomination to the position, made by President Barack Obama last September, had been held up in the Senate by Republican Kansas Sen. Pat Roberts, who wanted assurances from the administration that detainees at Guantanamo Bay would not be transferred to the U.S. military prison at Ft. Leavenworth in Kansas as part of the administration's policy to try and close the prison in Cuba.

Speaking on the Senate floor Tuesday afternoon, Roberts said he had received assurances during a meeting with Deputy Defense Secretary Robert Work that the administration would be unable to transfer any detainees to the United States from Guantanamo Bay because funding prohibitions from Congress for such moves remain in place.

"I look forward to voting for Mr. Fanning, who has always had my support for this position," Roberts said. "My hold was never about his courage, character or capability, but rather about our nation's security if the detainees were moved to Ft. Leavenworth."

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Fanning previously served as Defense Secretary Ash Carter's chief of staff, and also served as under secretary of the Air Force and deputy undersecretary of the Navy.

"I want to congratulate Eric Fanning on his confirmation as secretary of the Army by the U.S. Senate," Carter said. "Eric is one of our country's most knowledgeable, dedicated, and experienced defense officials and I am confident he will make an exceptional secretary. Eric's experienced leadership will be an invaluable asset to the Army at this important moment. I appreciate his willingness to serve and his continued commitment to our men and women in uniform."

And likely Democratic nominee Hillary Clinton added her support in a tweet Wednesday afternoon.

"The first openly gay leader of a U.S. military branch—a milestone we can all be proud of. Congrats, @SECARMY," she said.